To facilitate processing of most resin compositions (e.g. acrylonitrile-butadiene-styrene resins, polystyrene resins, polyamide resins and rigid or plasticized polyvinylchloride (PVC) resins) lubricants are required if useful and uniform finished products are to be obtained. Lubricants play a particularly important role in the extrusion, injection molding and blow molding of rigid PVC resin compositions.
Both internal and external lubrication is essential to maintain acceptable rheological properties of the melt throughout the processing and to obtain a useful finished product. Internal lubrication operates within the melt to reduce the melt viscosity of the polymer at the processing temperatures and improve the flow characteristics of the materials so that a high output of resin is possible using a minimum amount of work and without destroying the physical properties of the resin. External lubrication is required to reduce friction and sticking at the interface between the plastic melt and the metal surfaces of processing equipment in order to obtain a consistently uniform product having a smooth finish and essentially free of surface defects.
Emphasis has recently been shifted to developing new and better lubricant compounds which meet all the lubrication requirements for the processing of PVC and other resins, that is, function both as an internal and external lubricant. U.S. Pat. No. 3,578,621, for example, discloses diesters of the formula ##STR1## wherein R is an alkyl radical having 15 to 30 straight chain carbon atoms and R.sub.1 is an alkylene or alkenylene radical having 2 to 12 straight-chain carbon atoms and indicates that these compounds exhibit combined internal and external lubricating properties. Diesters of the above types are prepared by reacting monocarboxylic acids having 16 to 30 carbon atoms arranged in a straight-chain with dihydric alcohols having 2 to 12 carbon atoms. The diesters of the U.S. Pat. No. 3,578,621 are limited to those derived from pure monocarboxylic acids. Diesters obtained from mixed acids (montan wax esters are specifically mentioned) are indicated to be ineffective internal-external lubricants in the U.S. Pat. No. 3,578,621. Mixed acids (montanic acids) having a broad molecular weight distribution are obtained from montan wax and esters thereof are reported in the literature and commercially available. The montanic acids are mixed monocarboxylic acids typically containing from about 22 to 36 carbon atoms, with the predominant acids falling in the C.sub.26 - C.sub.32 carbon atom range. The bulk of the monocarboxylic acids derived from montan wax are straight-chain and contain an even number of carbon atoms. The acids are obtained from montan wax by saponification and separation of the resulting soaps from the unsaponifiable materials. They are also obtainable by the chromic acid oxidation of montan wax.